The present invention relates to a storage system, and more particularly to a method, apparatus, and system for remote file sharing in which double-written data can be shared from respective higher-level devices connecting to storage controllers in a storage system where data on a storage medium is double-written between the storage controllers without involvement by the higher-level devices in particular.
A technique for transferring data between storage controllers to double-write the data between the storage controllers without involvement by higher-level devices, that is to say, remote double recording, is described in U.S. Pat. No. 5,155,845. In this prior art, when a main storage controller receives, from a higher-level device, a main/secondary specification command specifying that the storage mediums under the control of the storage controllers are used as main and secondary storage mediums for example, the main storage controller copies data stored in the storage medium of the main storage controller to a storage medium of a secondary storage controller. When the higher-level device issues a write request to the main storage controller together with the main/secondary specification, the main storage controller stores the data, which should be written, in the main storage controller, and then issues a write request to the secondary storage controller.
The above-mentioned operation realizes the remote double recording. Even if a disaster or a failure causes the main storage controller to be incapable of inputting/outputting data, the remote double recording permits continuous operation using a secondary system comprising a higher-level device, and a secondary storage controller connecting to the higher-level device.
On the other hand, there is known a technique for sharing, from a plurality of higher-level devices, data stored in a storage medium under a storage controller; that is to say, this technique is called a file-sharing system. In this prior art, when a higher-level device issues a data write request to a storage controller, the storage controller stores data, which is transferred from the higher-level device, in a subordinate storage medium. When another higher-level device issues a request for reading/writing the data during the write processing, the another higher-level device which has issued the request is reported that because the storage controller is writing the data, the data cannot be accessed. As a result of the processing described above, when the another higher-level device issues a request for reading the data while the data from the former higher-level device is being written to the storage controller, the data is not read before the writing is completed. Even if the another higher-level device issues a request for writing the data, the data is not written before the writing is completed.
The operation described above permits the plurality of higher-level devices to share data under the storage controller. Sharing a file among the plurality of higher-level devices enables distributed processing, which reduces a processing load of each higher-level device.
Japanese Patent Laid-Open No. Hei 10-269030 discloses a remote file-sharing system that performs remote double recording between storage controllers and also permits a respective higher-level device to share a file.